This invention relates to an electrical machine consisting of a stator, which is made up of stacks of plates rotated into mutually offset positions and provided with axial channels, and of a rotor mounted on the ends of the machine and rotatable in the stator.
As the rotating internal rotor of electrical machines is round it is appropriate that the external diameter of the stator likewise, and not only the boring of the stator, should be made circular. In order to limit the eddy current losses the stator plates of rotary field machines are stamped out of sheet or strip metal and then combined to form a stack. At the present stage of technical progress the difference between the square containing the circular piece and this latter itself, i.e. 21% of the electric sheet, has to be scrapped, then having only about 5% of the original value of the material. Energy has to be consumed in the re-melting and further processing of the scrap.
As the conversion of electrical energy into mechanical energy and vice versa causes losses which heat up the machine and may cause the electrical insulation to burn out, measures have to be taken to ensure the effective dissipation of heat losses. At the present time this is done, in the case of surface-cooled machines, by means of housings which have numerous axial cooling ribs and over which a current of air passes in the axial direction and which are made of light metal or grey cast iron, the cylindrical stacks of stator plates being pressed into these housings. Not only raw materials are required for the production of the housings but also a considerable amount of energy for the melting, casting and cutting. Rising raw material and energy prices now make it necessary to consider whether the present method of construction, particularly for closed surface-cooled electrical machines can still be regarded as satisfactory under modern conditions.
A type of stator stack has become known in which the stamping lattice remained on the stator plates and axial cooling channels were cut into the diagonals of the square stack. A further system is known in which plates stamped in this manner are stacked with a continuously adjusted angle of rotation, the spaces thus formed between the ribs being filled up with light metal or casting resin. This leads to variants, without housings, of the present-day machines with axial ribs. Owing to the fact that the axial cooling channels have to be punched out, however, there is still a considerable part of the present stamping lattice that has to end as scrap. The operation of punching out axial cooling channels does not by itself always have the desired effect. Neither does the surface of the axial channels dissipate the heat loss to a sufficient extent.
In a further type of electrical machine, particularly of the kind in which the machine shaft is horizontal and the heat loss is dissipated by natural convection, the stator plates are in separate stacks, some of them having the usual round contour and the rest having the shape of the surrounding square. Here again, over 10% of the electric sheet used has to be scrapped.